This application claims the priority of German Patent Document 199 12 317.9, filed Mar. 19, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for automatically controlling the fraction of the exhaust gas quantity returned to an internal-combustion engine with respect to the mixture quantity which is fed on the whole to the internal-combustion engine and which is formed by the returned exhaust gas quantity and a fresh air quantity. Furthermore, the invention relates to a system for implementing the process.
Processes of the above-mentioned type are known, for example, from European Patent Document EP 05 74 614 A1, German Patent Document DE 43 37 313 C1 or German Patent document DE 42 38 068 A1.
The returning of exhaust gas, which leaves an internal-combustion engine after the combustion has taken place, and its mixing with the fresh air quantity flowing to the internal-combustion engine is used for lowering the temperature during the combustion operation, whereby the NOx emissions of the internal-combustion engine can be reduced. In practice, the exhaust gas return is used mainly in the case of diesel internal-combustion engines, but it can also be carried out in the case of Otto internal-combustion engines.
The quantity or the mass of the returned exhaust gas considerably influences the combustion operation taking place in the internal-combustion engine, and the air ratio xcex, the emitted pollutants (essentially NOx) as well as the efficiency of the combustion operation depend on this exhaust gas mass. A mass of returned exhaust gas which is not optimal can therefore result in unacceptably high pollutant emissions or in a steep rise of the fuel consumption. For this reason, it is meaningful to very precisely coordinate the quantity of the returned exhaust gas with each operating point of the internal-combustion engine when designing an internal-combustion engine.
The so-called exhaust gas return rate is used as a measurement for this purpose. This exhaust gas return rate is defined by the quotient of the returned exhaust gas quantity divided by the mixture quantity fed on the whole to the internal-combustion engine. The total mixture quantity returned to the internal-combustion engine is composed of the returned exhaust gas quantity and the fresh air quantity. In a known manner, the returned exhaust gas quantity can in this case be adjusted by so-called exhaust gas return valves which are controlled by the electronic system of the engine.
However, in the case of such exclusively controlled systems, no feedback takes place to the engine timing unit concerning the actually set exhaust gas return rate or the actual fraction of the returned exhaust gas quantity with respect to the total mixture quantity fed to the internal-combustion engine, whereby systematic faults, such as the hysteresis of a valve, a malfunctioning or disturbance affecting the system from the outside cannot be recognized and can therefore not be compensated. A precise adjustment of the returned exhaust gas quantity is therefore not generally ensured. As mentioned above, this results in increased exhaust gas emissions and a rising fuel consumption.
In various solution setups, for example, according to the above-mentioned documents, it was attempted to eliminate these problems by a determination of the actual fraction of the returned exhaust gas quantity and a corresponding automatic control thereof.
In European Patent Document EP 05 74 614 A1, the quantity of the returned exhaust gas is determined using a Venturi nozzle.
German Patent Document DE 43 37 313 C1 suggests a heat accumulator for evening out the exhaust gas temperature as well as a pressure gauge, a temperature measuring device and a control valve downstream of the heat accumulator. By means of these elements, the returned exhaust gas flow rate is to be determined and automatically controlled by a control valve.
In German Patent Document DE 42 38 068 A1, the pressure is measured in the exhaust pipe and the exhaust gas return rate is automatically controlled correspondingly.
If, for example, a commercially available xcex-probe is used as the sensor, it is disadvantageous that, below a minimal measurable temperature of approximately 150xc2x0 C., the heating capacity of the sensor is not sufficient for reaching the operating temperature required for the measurement, which results in high measuring inaccuracies. Another problem is the measuring inaccuracy of xcex-probes at oxygen concentrations of more than 19%. Particularly at a partial load, in which high oxygen concentrations occur, the determined exhaust gas return rate can therefore not be considered to be reliable. However, if the exhaust gas return rate is not correctly determined, it will not be possible to automatically precisely control it.
In the case of the automatic control by way of the pressure in the exhaust pipe, the pressure difference between the exhaust gas removal and the exhaust gas feeding is not constant, which results in a difficult automatic control. Furthermore, measuring inaccuracies can result, for example, from the contamination of the air filter, which measuring inaccuracies result in an incorrectly set exhaust gas return rate.
It is therefore an object of the present invention to provide a process by means of which the fraction of the exhaust gas quantity returned to an internal-combustion engine with respect to the mixture quantity returned on the whole to the internal-combustion engine can be determined in a very simple manner and, in addition, very precisely and, corresponding to the calculated actual fraction, can be automatically controlled to a predetermined desired fraction.
According to the invention, this object is achieved by providing a process for automatically controlling the fraction of the exhaust gas quantity returned to an internal-combustion engine with respect to the mixture quantity fed on the whole to the internal-combustion engine, which mixture quantity is formed by the returned exhaust gas quantity and a fresh air quantity,
wherein the actual fraction of the returned exhaust gas quantity with respect to the mixture quantity fed on the whole to the internal-combustion engine is determined by means of sensors from measurements of the temperature of the fed fresh air quantity, the temperature of the returned exhaust gas quantity and the temperature of the mixture quantity fed on the whole, and
wherein this actual fraction of the returned exhaust gas quantity is adapted to a predetermined desired fraction.
As the result of the temperature of the fed fresh air quantity, the temperature of the returned exhaust gas quantity and the temperature of the mixture quantity fed on the whole, the actual fraction of the returned exhaust gas quantity can be determined in a very simple manner according to the formula ARactual=(TLxe2x88x92TG)/(TLxe2x88x92TR). As the result of a corresponding automatic control, the actual fraction of the returned exhaust gas quantity determined in this manner can then be adapted to a predetermined desired fraction, for example, filed in a characteristic diagram.
A constructive system for implementing the above noted process according to the invention includes an internal-combustion engine, with which at least one fresh air pipe and at least one exhaust pipe are connected,
an exhaust gas return valve arranged in an exhaust gas return pipe,
a temperature sensor for measuring the temperature of the fed fresh air quantity,
a temperature sensor for measuring the temperature of the returned exhaust gas quantity, and
a temperature sensor for measuring the temperature of the mixture quantity fed on the whole.
As the result, a very simple arrangement exists in the periphery of an internal-combustion engine, whereby the process according to the invention can be carried out with a high reliability.
An alternative solution of the object of the invention involves a process for automatically controlling the fraction of the exhaust gas quantity returned to an internal-combustion engine with respect to the mixture quantity fed on the whole to the internal-combustion engine, which mixture quantity is formed by the returned exhaust gas quantity and a fresh air quantity,
wherein the actual fraction of the returned exhaust gas quantity with respect to the mixture quantity fed on the whole to the internal-combustion engine is determined by means of at least one sensor from at least one measurement of the temperature of the exhaust gas flowing out of the internal-combustion engine, and
wherein this actual fraction of the returned exhaust gas
quantity is adapted to a predetermined desired fraction, said system comprising:
an internal-combustion engine, with which at least one fresh air pipe and at least one exhaust pipe are connected,
an exhaust gas return valve, and
at least one temperature sensor for measuring the temperature of the exhaust gas flowing out of the internal-combustion engine.
In this case, the actual fraction of the returned exhaust gas quantity can be determined by the temperature of the exhaust gas flowing out of the internal-combustion engine. The reason is that the inventors surprisingly found a significant linear dependence of the returned exhaust gas quantity on the exhaust gas temperature. If, in this case, other factors, which influence the temperature of the exhaust gas flowing out of the internal-combustion engine, such as a raised intake air temperature, are recognized by the control of the internal-combustion engine, a very simple determination of the returned exhaust gas quantity is obtained, in which case the relationships may be filed, for example, in a characteristic diagram. By means of the determined actual fraction, an automatic control to the desired fraction will then be easily possible.
A constructive solution for implementing the process according to this alternative solution has an internal-combustion engine, with which at least one fresh air pipe and at least one exhaust pipe are connected,
an exhaust gas return valve, and
at least one temperature sensor for measuring the temperature of the exhaust gas flowing out of the internal-combustion engine.
Because of the only one required temperature sensor, a particularly simple construction of the system according to the invention is obtained which is resistant to disturbances.
Another alternative solution of the object of the invention involves a process for automatically controlling the fraction of the exhaust gas quantity returned to an internal-combustion engine with respect to the mixture quantity fed on the whole to the internal-combustion engine, which mixture quantity is formed by the returned exhaust gas quantity and a fresh air quantity,
wherein an actual fraction of the returned exhaust gas quantity with respect to the mixture quantity fed on the whole to the internal-combustion engine is determined by measurements of the flow rate of the fresh air quantity fed to the internal-combustion engine and of the flow rate of the mixture quantity fed on the whole to the internal-combustion engine, and
wherein this actual fraction of the returned exhaust gas quantity is adapted to a predetermined desired fraction.
Also, as the result of the measuring of the fresh air fed to the internal-combustion engine in relationship to the air mass fed on the whole to the internal-combustion engine, which air mass can be computed in a very simple manner from the displacement, a precise determination of the returned exhaust gas quantity can be carried out.
A constructive solution for the implementation of this last mentioned process has an internal-combustion engine, with which at least one fresh air pipe and at least one exhaust pipe are connected,
an exhaust gas return valve arranged in the exhaust gas return pipe,
at least one air flow rate measuring device for measuring the flow rate of the fresh air quantity fed to the internal-combustion engine provided in the fresh air pipe,
at least one pressure sensor for measuring the pressure of the mixture quantity fed on the whole to the internal-combustion engine, and
at least one temperature sensor for measuring the temperature of the mixture quantity fed on the whole to the internal-combustion engine.
In the case of this system according to the invention, preferably only components are used which are very easy to handle and ensure reliable measuring results.
Another alternative solution achieving the object of the invention is a process for automatically controlling the fraction of the exhaust gas quantity returned to an internal-combustion engine with respect to the mixture quantity fed on the whole to the internal-combustion engine, which mixture quantity is formed by the returned exhaust gas quantity and a fresh air quantity,
wherein the returned exhaust gas quantity is automatically controlled to a predetermined content of nitrogen oxides in the exhaust gas.
As the result of the automatic control of the returned exhaust gas quantity by way of the nitrogen oxide content in the exhaust gas, this value, which should not exceed a certain limit value, can be used directly as an input value for an automatic control.
A constructive solution for implementing this last mentioned includes a said system comprising:
an internal-combustion engine, with which at least one fresh air pipe and at least one exhaust pipe are connected,
an exhaust gas return valve arranged in an exhaust gas return pipe, and
at least one sensor for measuring the fraction of the nitrogen oxides in the exhaust gas.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.